1. Field of the Invention
The invention relates to the field of digitally controlling video displays.
2. Prior Art
With the reduced costs of large scale integrated circuits, it has become possible to provide low cost microcomputers suitable for home use. One such use which has flourished in recent years is the application of microcomputers to video displays for games, graphic displays and the like. Most often an ordinary television receiver is employed as the video display means. The standard, raster scanned cathode ray tubes employed in these receivers present unique problems in the interconnecting of these displays with the digital information provided by the microcomputer.
These receivers are designed to operate with one or more standard video broadcasting schemes such as PAL. In copending application Ser. No. now U.S. Pat. No. 4,136,359 786,197, filed Apr. 11, 1977, entitled "Microcomputer For Use With Video Display", and assigned to the assignee of this application, a digitally controlled display is described. This earlier filed application deals in part with the generation of color signals for the television broadcasting system employed in the United States and some other countries, referred to as the National Television Systems Committee (NTSC) standard.
In many parts of the world and particularly in Europe, a phase alternation line (PAL) system is employed for television broadcasting. The PAL raster scan displays employ different signals (e.g. different frequencies, format, etc.) than the NTSC standard. The subject of this application is a unique means for generating color signals in a digital manner which are compatible with a PAL display such as an ordinary PAL compatible television receiver.